2006 Pacifica
 

I have a 2006 Pacifica that is throwing an output speed sensor fault P0720. Replaced the sensor but the problem is happening. THE BIG QUESTION?
The problem is when the climate control is on. The vehicle will not shift, and when you are at a stop in gear (drive) the speedometer jumps between 20 and 30 mph and the vehicle surges and makes a clunking sound. If I turn the climate control off the vehicle drives and shifts perfectly. If anyone has had this problem and can steer me in the right direction I would be forever in their debt.

u have a shorted wire touching together if say where the ac compressor is on the volts to the clutch are bleeding over to the speed sensor side.

Thanks for the thought, I have already thought of this but can't determine by the wiring diagrams where this would or could be happening. I think this may be in the BCM or computer. By the wiring diagrams the two systems do not seem to share any connectors or common wiring except in the BCM

two things your trying to compare what you see to what the sensors are throwing at you. The cluster is nothing but a computer doing whats its told. So if you have a sensor having issues and it relays this back to the pcm the pcm then in turns relays this same info over the bus network and well computer like the bcm and cluster and tcm pick up on this info and you see what you see on the display. The bcm does not control the spedo the cluster does. The ac clutch wire harness is in that big loom to the right of the solenoid pack along with the wires for the input and output speed sensor. SO when you turn on the ac control the power to the clutch is applied and its feeding back to the pcm via the speed sensors wires.